[R] Assigning to a vector while keeping the attributes

[David Winsemius]

Not sure what "a" really is. It's not a vector or a list according to  
the R interpreter.

 > a <- structure(1:3,x=3)
 > mode(a)
[1] "numeric"
 > is.vector(a)
[1] FALSE
 > is.list(a)
[1] FALSE

Experimentation shows that simple indexing provides the functionality  
you request while append does not.

 > a[4] <- 10
 > a
[1]  1  2  3 10
attr(,"x")
[1] 3


 > a <-append(a, 20)
 > a
[1]  1  2  3 10 20

# appears to have now coerced it to a vector
 > a
[1]  1  2  3 10 20
 > is.vector(a)
[1] TRUE

-- 
David Winsemius
On Feb 9, 2009, at 7:09 AM, Alon Wasserman wrote:

> Hi,
> I would like to know how to assign values to a whole vector while  
> keeping
> its attributes. For example, say I have
> a <- structure(1:3,x=3)
> and I want to change the values to 2:4. If I do, a <- 2:4, the  
> attribute x
> will be lost. I have a workaround for this case, which is to use  
> subset
> assignment
> a[1:3] <- 2:4.
> However, what if I want to also change the length of a? Then this  
> workaround
> doesn't work and also assigning into length(a) drops the attributes.  
> More
> severe workarounds (such as keeping the attributes and then  
> reassigning
> them) work, but if there's a simple solution, I'd be happy to use it.
> Thanks,
> Alon
>
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